Suma,
International law is pretty much a joke. The reality of law is that sovereignty creates law. There's a law of Pennsylvania, a law of the USA, French law, Australian law and German law. There is no international law; it's a voluntary thing.
International law, such as it is, only exists as long as signatories to certain treaties decide that they wish to be bound by them. And who says regime change isn't allowed under international law? In 1950 the North Koreans invaded the South and pushed all the way to the Pusan perimeter. They effectively were The Regime over 95% of the Korean peninsula. The UN went in (well, the US went in, with a coalition) and changed that regime back to the Yalu. Then the Chinese came in and changed the regime back to the 38th parallel. Finally we had regime redux.
As for Guantanamo, Abu Greib and the Geneva Convention; I'm sure some rules were technically violated, but not as many as you might think. The Geneva Convention only applies to uniformed combatants, not insurgents, folks packing heat under djellabahs, etc.
Be careful not to buy into broad conclusory phrases "regime change is not allowed under internatioal law". It ain't necessarily so.
Kb |